The HI93719 is a portable meter providing measurement of Ca and Mg Hardness. Water, with exception of distilled water, contains dissolved salts (Magnesium and Calcium carbonates). The presence of dissolved salts is due to the fact that water comes from underground, and it is in turn made up by rainfalls. By passing through the various layers of soil and rocks, rain water dissolves some of the mineral substances. Hardness is a consequence of the type of rock layers which the water passes through and of its permanence in the water bearing stratum.